IL4 and IL13 are related cytokines that show a significant sequence identity [1,2] and share numerous biological activities. Both have been shown to be important in the induction of IgE and IgG4 synthesis in human B cells [3-6] and the differentiation of Th cells into a Th2 phenotype [8,11]. Among the events leading to IgE synthesis by B cells, induction of germline xcex5 RNA transcription, which precedes the class switching to the corresponding H chain C region, has been shown to be triggered by IL4 and IL13 [6,9,10]. Th cells can be subdivided into two major subtypes according to their cytokine production capacities [11]. The major distinction between the two phenotypes are the capacity of Th1 cells to secrete IFNxcex3 and Th2 cells to produce IL4 and IL5 [11]. Th2 cells are thought to be implicated in the development of atopy, allergy and some forms of asthma [12,13]. The differentiation of Th cells into the Th2 phenotype can be induced by IL4 [11]. IL13 was first considered as to be inactive on T cells [2]. However it has been shown recently to induce the differentiation of murine Th cells into the Th2 phenotype [8].
In addition to their effects on lymphocytes, IL4 and IL13 share the ability to inhibit the production of inflammatory cytokines by macrophages [1,2] and to up-regulate the expression of the vascular cell adhesion molecule-1 (VCAM-1) on endothelial cells [16,17,18] leading to adhesion and trans-endothelial migration of very late antigen 4 (VLA4) expressing leukocytes [19]. This provides a basis for selective extravasation of eosinophils, the hallmark of the inflammatory pathology seen in allergy and asthma [20,58,59].
These two cytokines activate common cytokine receptor signaling pathways involving 4PS/IRS-1 [21-25] and the signal transducer and activator of transcription 6 (STAT-6; ref. 26-28). In the murine system, inactivation of STAT-6 has been demonstrated to affect both IL4 and IL13 signaling and to block IL4 and IL13-induced IgE synthesis or Th2 differentiation [29-31]
Studies have been conducted to examine if these two cytokines share a receptor or receptor subunits [2,18,32-34]. The IL4R is composed of two chains, the IL4Rxcex1 chain and the common xcex3 chain (xcex3c) The xcex3c is shared with the receptors of many of the other 4-helix bundle cytokines such as L2, IL4, IL7, IL9 and IL15 [35,36]. The IL4Rxcex1 chain alone forms a tight complex with its ligand, whereas the xcex3c was thought to be mainly responsible for signal transduction. However, IL4- and IL-3-induced responses could be observed in cells which naturally do not express xcex3c or in lymphocytes obtained from severe combined immunodeficiency (SCID) patients who are deficient for xcex3c [34,37-39]. It has therefore been proposed that a second form of an IL4R exists which would be activated by both IL4 and IL13 (IL4R type II/IL13R: ref. 40).
A cDNA encoding for a human IL-13 receptor xcex1 chain (IL-13 Rxcex1) has been cloned (Caput et al [42]). IL-13 R xcex1 has been shown to participate in the type II IL-4 receptor which also contains an IL-4 R xcex1 chain.
The present inventors have now cloned from a human tissue source a cDNA encoding a polypeptide capable of binding human IL-13 which has not previously been identified. This polypeptide has only 27% sequence identity with the polypeptide identified by Caput et al. Furthermore the expression pattern of mRNAs encoding the molecule identified by the present inventors is very different from that of the molecule identified by Caput er al.
According to one aspect of the present invention there is provided a polypeptide which is capable of binding human IL-13 and/or of binding human IL-4 in the presence of IL4 R xcex1; which:
a) comprises the amino acid sequence shown in FIG. 1;
b) has one or more amino acid substitutions, deletions or insertions relative to a polypeptide as defined in a) above; or
c) is a fragment of a polypeptide as defined in a) or b) above which is at least ten amino acids long and which is preferably at least fifty amino acids long.
The term xe2x80x9cpolypeptidexe2x80x9d is used herein in a broad sense to indicate that there are a plurality of peptide bonds present. It therefore includes within its scope substances which may sometimes be referred to in the literature as peptides, polypeptides or proteins.
It can be determined by using techniques known in the art whether or not a particular polypeptide is capable of binding human IL-13. For example, by binding the polypeptide to radiolabelled or tagged forms of human IL-13 or by competitive inhibition of the binding of radiolabelled or tagged forms of human IL-13 to its natural receptor. The binding affinity of the polypeptide for human IL-13 is preferably less than 10 xcexcM, more preferably less than 1 xcexcM (when determined at 37xc2x0 C.).
Polypeptides within the scope of the present invention may be capable of binding human IL-4. This can also be determined by using techniques known to those skilled in the art. For example, by binding the polypeptide to radiolabelled or tagged forms of human IL-4 or by competitive inhibition of the binding of radiolabelled or tagged forms of human IL-4 to its natural receptor. The affinity of the polypeptide would be in the xcexcM. ideally nM range.
Preferred polypeptides of the present invention form a moiety when combined with the IL-4 R xcex1 chain which is capable of binding IL-4 and/or IL-13. This moiety is within the scope of the present invention and is preferably membrane bound. It may represent a new form of IL-4 receptor (referred to herein as IL-4 type II receptor) and be useful in studying the structure and function of said receptor.
The polypeptides of the present invention which are capable of binding human IL-13 and/or human IL-4 are useful for a number of other purposes.
For example, they can be used to bind human IL-4 or human IL-13 and thereby to act as inhibitors by interfering with the interaction between human IL-13 or human IL-4 and their natural receptors. This is useful in medicine since it can be used in the treatment of diseases in which human IL-4 or human IL-13 are responsible (at least partially) for adverse effects in a patient. For example, polypeptides of the present invention could be used to inhibit IL-13 or IL-4 induced IgE synthesis in B cells. This is useful in the treatment of diseases where IgE or Th2 differentiation plays a rolexe2x80x94e.g. in the treatment of atopy, atopic dermatitis, allergies, rhinitis, eczema, asthma or AIDS.
Polypeptides of the present invention may therefore be used in the treatment of a human or non-human animal. The treatment may be prophylactic or may be in respect of an existing condition. Examples of particular disorders which can be treated are discussed supra.
Thus a polypeptide of the present invention may be used in the manufacture of a medicament for the treatment of one or more disorders.
The medicament will usually be supplied as part of a pharmaceutical composition. which may include a pharmaceutically acceptable carrier. This pharmaceutical composition will usually be sterile and can be in any suitable form, (depending upon the desired method of administering it to a patient).
It may be provided in unit dosage form, will generally be provided in a sealed container, and can be provided as part of a kit. Such a kit is within the scope of the present invention. It would normally (although not necessarily) include instructions for use. It may include a plurality of said unit dosage forms.
Pharmaceutical compositions within the scope of the present invention may be adapted for administration by any appropriate route, for example by the oral (including buccal or sublingual), rectal, nasal, topical (including buccal, sublingual or tansdermal), vaginal or parenteral (including subcutaneous, intramuscular, intravenous or intradermal) route. Such a composition may be prepared by any method known in the art of pharmacy, for example by admixing the active ingredient with a carrier under sterile conditions.
The pharmaceutical compositions may contain one or more of the following: preserving agents, solubilising agents, stabilising agents, wetting agents, emulsifiers, sweeteners, colourants, odourants, salts (substances of the present invention may themselves be provided in the form of a pharmaceutically acceptable salt), buffers, coating agents or antioxidants. They may also contain therapeutically active agents in addition to the substance of the present invention.
In addition to the medical uses, polypeptides of the present invention can be used in the production of diagnostic agents. For example they can be used in the production of antibodies which can in turn be used in the diagnosis of various disorders. Antibodies and their uses are discussed in greater detail below under the heading xe2x80x9cUses in raising or selecting antibodiesxe2x80x9d.
The polypeptides themselves may be used for diagnosis. For example they could be used to diagnose the presence of mutated forms of IL-4 or IL-13 which do not bind to their natural receptors. This could be done by providing polypeptides of the present invention which act like a natural receptor in binding to wild-type human IL-4 or human IL-13 but which will not bind to mutated forms of IL-4 or IL-13 which do not bind to the corresponding natural receptor. As a positive control, wild type IL-4 or IL-13 could be used.
Polypeptides of the present invention can also be used in screening. (Substances identified as being useful for a given purpose by such screening are within the scope of the present invention when used or indicated as being useful for such a purpose.)
For example, polypeptides capable of binding IL-4 or IL-13 can be used to screen for substances capable of inhibiting the action of human IL-4 or human IL-13 (e.g. by competitive or non-competitive binding to the respective natural receptor). Such substances agents are useful in the treatment of the diseases discussed supra.
Alternatively, they can be used to screen for substances which act as agonists of human IL-4 or human IL-13.
Polypeptides of the present invention which bind human IL-4 or human IL-13 are therefore useful in screening for substances which could be useful in treating cancer or inflammatory diseases (e.g. rheumatoid arthritis and inflammatory bowel disease), multiple sclerosis. Alzheimer""s disease, Lupus erythromatosus, thyroiditis, diabetes, uveitis, dermatitis, psoriasis, urticaria, nephrotic syndrome, glomerulonephritis, inflammatory bowel disease, ulcerative colitis, Crohn""s disease, Sjogren""s syndrome, toxoplasmosis, listeriosis, leprosy, Lyme disease, tuberculosis, malaria, leichmaniasis.
As will be appreciated by the skilled person, in some of the uses discussed above, polypeptides which can bind human IL-13 or human IL-4 but which does not necessarily have other functional regions, other than the IL-13 or IL-4 binding region can be used. Such polypeptides are therefore within the scope of the present invention.
Thus the polypeptides may be xe2x80x9csolublexe2x80x9d, i.e. in a form which enables them to be provided as extracellular polypeptides rather than membrane-bound polypeptides. Such polypeptides do not possess regions which would cause them to become anchored in a membrane. Thus they will generally not include hydrophobic domains which can give rise to the tnansmembrane regions in membrane-bound proteins. They will also generally not include regions which are normally located in the cytoplasm of a cell (e.g. regions involved in transmitting a cytoplasmic signal from a receptor following the binding of an interleukin to an extracellular part of that receptorxe2x80x94such regions are referred to herein as xe2x80x9csignal transmitting regionsaxe2x80x9d.)
For example, the extracellular region of the polypeptide having the sequence shown in FIG. 1 (SEQ ID NO:8 and SEQ ID NO:9) could be used on its own as a soluble polypeptide capable of binding human IL-13 or human IL-4. Furthermore, one or more amino acid substitutions, insertions and/or deletions relative to said polypeptide could be made to provide other soluble polypeptides capable of binding human IL-13 or human IL-4. Indeed a skilled person could use protein binding studies to determine which part of said polypeptide is involved in binding human IL-13 and/or human IL-4. This could be done by scanning, directed or deletion mutagenesis, crosslinking with the ligands followed by protease digestion and sequencing, X-ray crystallography of the cytokine-receptor complex, epitope mapping of blocking antibodies, phage display libraries. Parts of the polypeptides having the sequence shown in FIG. 1 which are not involved in binding could therefore be identified and could be omitted when producing other polypeptides within the scope of the present invention.
One or more amino acid substitutions, deletions and/or insertions relative to said sequences may therefore be made in order to produce other polypeptides which may be capable of binding IL-4 or IL-13.
Soluble polypeptides of the present invention are likely to be especially useful in binding to IL-13 or IL-4 in a patient""s circulatory system, thereby preventing bound IL-4 or IL-13 interacting with their receptors. Bound IL-4 or IL-13 could then be removed from a patient. For example immobilised antibodies having a high degree of specificity for the soluble polypeptides could be used. (It may however be possible to use membrane bound polypeptides for this and for the other purposes where soluble polypeptides are useful. For example liposomes comprising membrane bound polypeptides could be used. Like the polypeptides of the present invention they can flow with liquids and can therefore move through a patient""s circulatory system. Such liposomes may even have advantages of their ownxe2x80x94e.g. they can comprise a plurality of polypeptides of the present invention and can therefore be highly effective due to being xe2x80x9cmultivalentxe2x80x9d for polypeptides of the present invention.)
The soluble polypeptides of the present invention could be used in treating the diseases discussed above in which IL-4 or IL-13 are at least partially responsible for adverse effects in a patient (these diseases are discussed supra) since they can be easily introduced into a patient""s circulatory system and bind to IL-4 or IL-13.
They can also be used for screening purposes.
In some circumstances however it may be preferred to use polypeptides of the present invention which include in addition to an IL-13 or IL-4 binding region at least a signal transmitting region (e.g. where it is desired to screen for substances), e.g. agonists, capable of producing an IL-13 or IL-4 mediated response). In these circumstances membrane bound polypeptides will usually be particularly preferred.
It should be noted that the present invention is not limited to polypeptides which bind to IL-4 or IL-13 or to uses thereof. According to a further aspect of the present invention there is provided a polypeptide comprising a signal transmitting region (which can be involved in providing the intracellular signals in response to IL-4 or IL-13 binding to a receptor). Such a polypeptide can be used for screening purposes.
For example, it could be used in screening for substances which might inhibit signalling via an IL-13 or IL-4 receptor in vivo by preventing the action of cytoplasmic signalling molecules, e.g. kinases, STATs, IRS-1 or IRS-2 (IRS-1 and IRS-2 are discussed by Sun et al in Nature 377:173-177 (1995)). Alternatively it could be used to screen for substances which stimulate or improve such signalling in vivo.
An example of a polypeptide which could be used in such a manner is the polypeptide comprising the 59 amino acid cytoplasmic sequence of the polypeptide given in FIG. 1 (amino acids 368 t 427). Of course, one or more amino acid insertions, deletions or substitutions could be made relative to such a polypeptide to produce other polypeptides comprising a signal transmitting region. For example, a series of deletions could be made to identify the smallest part of the polypeptide consisting of the 59 amino acid sequence discussed above which could be used in screening. Such a part would also be a polypeptide within the scope of the present invention.
One or more amino acid substitutions and/or insertions could then be made to such a polypeptide to produce other polypeptides having a signal transmitting region. Such polypeptides would also be useful in screening.
Whatever polypeptides with a signal transmitting region are used, they are preferably provided in phosphorylated form. Desirably the tyrosine residues are phosphorylated. This can be achieved by treating the polypeptide with kinases or expressing them in cells or bacteria expressing appropriate kinases. Alternatively phosphopeptides can be synthesized chemically.
Whatever the nature of polypeptides of the present invention, they can be used in raising or selecting antibodies. The present invention therefore includes antibodies which bind to a polypeptide of the present invention. Preferred antibodies bind specifically to polypeptides of the present invention and can therefore be used to purify such polypeptides.
The antibodies described in the foregoing paragraph are within the scope of the present invention. They may be monoclonal or polyclonal.
Polyclonal antibodies can be raised by stimulating their production in a suitable animal host (e.g. a mouse, rat, guinea pig, rabbit, sheep, goat or monkey) when a polypeptide of the present invention is injected into the animal. If necessary an adjuvant may be administered together with the substance of the present invention. The antibodies can then be purified by virtue of their binding to a polypeptide of the present invention.
Monoclonal antibodies can be produced from hybridomas. These can be formed by fusing myeloma cells and spleen cells which produce the desired antibody in order to form an immortal cell line. Thus the well known Kohler and Milstein technique (Nature 256 52-55 (1975)) or variations upon this technique can be used.
Techniques for producing monoclonal and polyclonal antibodies which bind to a particular polypeptide are now well developed in the art. They are discussed in standard immunology textbooks for example in Roitt et al. Immunology second edition (1989). Churchill Livingstone. London.
In addition to whole antibodies, the present invention includes derivatives thereof which are capable of binding to polypeptides of the present invention. (The sections of this application which refer to antibodies therefore apply mutatis mutandis to derivatives thereof, unless the context indicates otherwise.)
Thus the present invention includes antibody fragments and synthetic constructs. Examples of antibody fragments and synthetic constructs are given by Dougall et al in Tibtech 12 372-379 (September 1994).
Antibody fragments include inter alia Fab, F(abxe2x80x2)2 and Fv fragments (these are discussed in Roitt et al [supra], for example).
Fv fragments can be modified to produce a synthetic construct known as a single chain Fv (scFv) molecule. This includes a peptide linker covalently joining Vh and V1 regions which contribute to the stability of the molecule.
Other synthetic constructs which can be used include CDR peptides. These are synthetic peptides comprising antigen binding determinants. Peptide mimetics may also be used. These molecules are usually conformationally restricted organic-rings which mimic the structure of a CDR loop and which include antigen-interactive side chains.
Synthetic constructs include chimaeric molecules. Thus, for example, humanised (or primatised) antibodies or derivatives thereof are within the scope of the present invention. An example of a humanised antibody is an antibody having human framework regions, but rodent hypervariable regions.
Synthetic constructs also include molecules comprising an additional moiety which provides the molecule with some desirable property in addition to antigen binding. For example the moiety may be a label (e.g. a fluorescent or radioactive label).
Alternatively, it may be a pharmaceutically active agent.
The antibodies or derivatives thereof of the present invention have a wide variety of uses. They can be used in purification and/or identification of polypeptides of the present invention. Thus they may be used in diagnosis.
For example, they can be used to evaluate the level of expression of IL-13 and/or IL-4 receptors in a given sample or to evaluate the pattern of expression in different cells or tissues. Abnormal levels or patterns of expression may be indicative of a disorder.
Such antibodies can be used to identify differences in IL-13 or IL-4 receptors which arise due to allelic variation between individuals in a population. This is useful in the identification of particular allelic variants which are associated with a given disease.
Antibodies against polypeptides of the present invention are also useful in identifying IL-13 or IL-4 receptors or parts thereof which have been shed from cells (as may occur in certain diseases) such as cancer, leukaemia atopy, atopic dermatitis, allergies, rhinitis, eczema, asthma. AIDS. Lupus erythromatosus, thyroiditis, diabetes, uveitis, dermatitis, psoriasis, urticaria, nephrotic syndrome, glomerulonephritis, inflammatory bowel disease, ulcerative colitis. Crohn""s disease, Sjogren""s syndrome, toxoplasmosis.
Antibodies are also useful in purification of polypeptides of the present invention. Preferred antibodies therefore have a high degree of specificity for polypeptides of the present invention.
The antibodies or derivatives thereof of the present invention can be provided in the form of a kit for screening for the polypeptides of the present invention.
From the foregoing discussions it will be appreciated that the present invention includes many polypeptides within its scope and that these polypeptides can be useful for a number of different purposes. Preferred polypeptides of the present invention are particularly useful for these purposes and can be identified as having substantial amino acid sequence identity with one or more of the following amino acid sequences:
a) the complete amino acid sequence shown in FIG. 1 (amino acids 1 to 427),
b) the cytoplasmic amino acid sequence shown in FIG. 1 (amino acids 368 to 427).
c) the extracellular amino acid sequence shown in FIG. 1 (amino acids 27 to 347).
Such polypeptides may have at least 50% amino acid sequence identity with one of the above. More preferably the degree of sequence identity is at least 60% or at least 70%. Most preferably the degree of sequence identity is at least 80% (e.g. at least 90%, at least 95% or at least 99%).
The degree of amino acid sequence identity can be calculated, for example, using a program such as xe2x80x9cbestfitxe2x80x9d (Smith and Waterman, Advances in Applied Mathematics, 482-489 (1981)) to find the best segment of similarity between any two sequences. The alignment is based on maximising the score achieved using a matrix of amino acid similarities such as that described by Schwarz and Dayhof (1979) Atlas of Protein Sequence and Structure. Dayhof, M. O., Ed pp 353-358.
Where high degrees of sequence identity are present there may be relatively few differences in amino acid sequence. Thus for example there may be less than 20 differences, less than 10 differences, or even only 1 amino acid difference.
The skilled person is in a position to provide useful preferred polypeptides with substantial amino acid sequence identity to the sequences given above since the skilled person is aware that one or more amino acid substitutions, insertions and/or deletions can often be made relative to a given sequence without losing desired characteristics (e.g. the capability of binding to human IL-4 or human IL-13 and/or the possession of a signal transmitting region.
The polypeptides of the present invention may be produced by techniques known to those skilled in the art. For example gene cloning techniques may be used to provide a nucleic acid sequence encoding such a polypeptide. By using an appropriate expression system (e.g. a eukaryotic, prokaryotic or cell free system) the polypeptide can then be produced. It can then be purified using standard purification techniques.
Alternatively, chemical synthesis techniques may be used to produce polypeptides of the present invention. Such techniques generally utilise solid phase synthesis. Chemical synthesis techniques which allow polypeptides having particular sequences to be produced have now been automated. Machines capable of chemically synthesising polypeptides are available, for example, from Applied Biosystems Ltd.
Various modifications which can be made to a specified polypeptide sequence will now be discussed.
A polypeptide may consist of a particular amino acid sequence, or may have an additional N-terminal and/or an additional C-terminal amino acid sequence.
Additional N-terminal or C-terminal sequences may be provided for various reasons. Techniques for providing such additional sequences are well known in the art. These include using gene cloning techniques to ligate nucleic acid molecules encoding polypeptides or parts thereof, followed by expressing a polypeptide encoded by the nucleic acid molecule produced by ligation.
Additional sequences may be provided in order to alter the characteristics of a particular polypeptide. This can be useful in improving expression or regulation of expression in particular expression systems. For example, an additional sequence may provide some protection against proteolytic cleavage. This has been done for the hormone Somatostatin by fising it at its N-terminus to part of the xcex2 galactosidase enzyme (Itakwa et al., Science 198: 105-63 (1977)).
Additional sequences can also be useful in altering the properties of a polypeptide to aid in identification or purification.
For example, a polypeptide may be linked to a moiety capable of being isolated by affinity chromatography. The moiety may be a pre-selected antigen or an epitope and the affinity column may comprise immobilised antibodies or immobilised antibody fragments which bind to said antigen or epitope (desirably with a high degree of specificity). The fusion protein can usually be eluted from the column by addition of an appropriate buffer.
Additional N-terminal or C-terminal sequences may, however, be present simply as a result of a particular technique used to obtain a substance of the present invention and need not provide any particular advantageous characteristic.
One or more substitutions deletions and/or insertions may be made relative to a specified polypeptide (which itself may include heterologous N-terminal and/or C-terminal as discussed above). These are discussed below:
(i) Substitutions
The skilled person is aware that various amino acids have similar properties. One or more such amino acids of a polypeptide can often be substituted by one or more other such amino acids without eliminating a desired characteristic of that s polypeptide.
For example, the amino acids glycine, alanine, valine, leucine and isoleucine can often be substituted for one another (amino acids having aliphatic side chains). Of these possible substitutions it is preferred that glycine and alanine are used to substitute for one another (since they have relatively short side chains) and that valine, leucine and isoleucine are used to substitute for one another (since they have larger aliphatic side chains which are hydrophobic).
Other amino acids which can often be substituted for one another include:
phenylalanine, tyrosine and tryptophan (amino acids having aromatic side chains);
lysine, arginine and histidine (amino acids having basic side chains);
aspartate and glutamate (amino acids having acidic side chains);
asparagine and glutamine (amino acids having amide side chains);
and cysteine and methionine (amino acids having sulphur containing side chains).
Substitutions of this nature are often referred to as xe2x80x9cconservativexe2x80x9d or xe2x80x9csemi-conservativexe2x80x9d amino acid substitutions.
(ii) Deletions
Amino acid deletions can be advantageous since the overall length and the molecular weight of a polypeptide can be reduced whilst still retaining a desired characteristic. This can enable the amount of polypeptide required for a particular purpose to be reduced. For example if the polypeptide is to be used in medicine, dosage levels can be reduced by using such polypeptides.
(iii) Insertions
Amino acid insertions relative to a given polypeptide sequence can be made e.g. to assist in identification, purification or expression; as explained above in relation to fusion proteins.
Polypeptides incorporating amino acid changes (whether substitutions, deletions or insertions) relative to the sequence of a polypeptide as defined in a) above can be provided using any suitable techniques. For example, a nucleic acid sequence incorporating a desired sequence change can be provided by site directed mutagenesis. This can then be used to allow the expression of a polypeptide having a corresponding change in its amino acid sequence.
In addition to the polypeptides of the present invention an d antibodies/antibody derivatives discussed above, the present invention also provides nucleic acid molecules.
Such nucleic acid molecules:
a) code for a polypeptide according to thee present invention: or
b) are complementary to molecules as defined in a) above or
c) hybridise to molecules as defined in a) or b) above.
These nucleic acid molecules and their uses are discussed in greater detail below:
The polypeptides of the present invention can be coded for by a large variety of nucleic acid molecules, taking into account the well known degeneracy of the genetic code. All of these molecules are within the scope of the present invention.
They can be inserted into vectors and can be cloned to provide large amounts of DNA or RNA for further study. Suitable vectors may be introduced into host cells to enable the expression of polypeptides of the present inventions using techniques known to the person skilled in the art. Alternatively, cell free expression systems may be used.
Techniques for cloning, expressing and purifying polypeptides are well known to the skilled person. Various techniques are disclosed in standard text books such as in Sambrook et al [Molecular Cloning 2nd Edition, Cold Spring Harbor Laboratory Press (1989)]; in Old and Primrose [Principles of Gene Manipulation 5th Edition, Blackwell Scientific Publications (1994); and in Stryer [Biochemistry 4th Edition, W H Freeman and Company (1995)].
By using appropriate expression systems different forms of polypeptides of the present invention may be expressed.
For example, the polypeptide may be provided in glycosylated or non-glycosylated form. Non-glycosylated forms can be produced by expression in prokaryotic hosts, such as E. coli, whereas glycosylated forms can be produced in eukaryotic hosts, such as S cerevisiae. 
Polypeptides comprising N-terminal methionine may be produced using certain expression systems, whilst in others the mature polypeptide will lack this residue.
Polypeptides may initially be expressed to include signal sequences. Different signal sequences may be provided for different expression systems. Alternatively signal sequences may be absent.
Polypeptides may be expressed with or without hydrophobic domains which can be used in anchoring Polypeptides in a cell membrane. Where it is desired to produce soluble polypeptides. such hydrophobic domains will not be present.
In addition to nucleic acid molecules coding for substances according to the present invention (referred to herein as xe2x80x9ccodingxe2x80x9d nucleic acid molecules), the present invention also includes nucleic acid molecules complementary thereto. Thus, for example each strand of a double stranded nucleic acid molecule is included within the scope of the present invention in addition to the double stranded molecule itself. Also included are mRNA molecules and complementary DNA molecules (e.g. cDNA molecules).
Nucleic acid molecules which can hybridise to any of the nucleic acid molecules discussed above are also covered by the present invention. Such nucleic acid molecules are referred to herein as xe2x80x9chybridisingxe2x80x9d nucleic acid molecules.
Hybridising nucleic acid molecules can be useful as probes or primers, for example.
Nucleic acid molecules may therefore be useful as in the analysis of allelic variation. One example of this is in the use of such molecules in identifying allelic variation in a region of a nucleic acid molecule encoding the signal peptide part of polypeptides according to the present invention.
The signal peptide area contains a long polyglycine stretch. The MRNA segment encoding for this poly G stretch forms GC reach repeats. The present inventors have observed deletions in this area when the cDNA was subjected to multiple cycles of polymerization (PCR) and believe that this region could lead to instability which would be a source of allelic variation. Allelic variation in this area could affect the expression of the IL-13 receptor and be involved in pathologies associated with disregulation of the IgE synthesis or T helper cell differentiation in the TH1-TH2 phenotype. such as an allergy. (This sequence area is not present in the murine counterpart.) Probes or primers which are poly G and or G-C rich molecules (or which are poly A or C-G rich in the case of complementary strands) are therefore particularly useful.
Desirably hybridising molecules of the present invention are at least 10 nucleotides in length and preferably are at least 25 or at least 50 nucleotides in length. The hybridising nucleic acid molecules may specifically hybridise to nucleic acids which code for a polypeptide of the present invention or which are complementary to nucleic acids molecules which code for a molecule of the present invention.
Preferred hybridising molecules hybridise to such molecules under stringent hybridisation conditions. One example of stringent hybridisation conditions is where attempted hybridisation is carried out at a temperature of from about 35xc2x0 C. to about 65xc2x0 C. using a salt solution which is about 0.9 molar. However, the skilled person will be able to vary such parameters as appropriate in order to take into account variables such as probe length, base composition, type of ions present, etc.
In addition to being used as probes, hybridising nucleic acid molecules of the present invention can be used as antisense molecules to alter the expression of substances of the present invention by binding to complementary nucleic acid molecules. This technique can be used in antisense therapy. Such molecules may also be used to produce ribozymes. Ribozymes can be used to regulate expression by binding to and cleaving RNA molecules which include particular target sequences.
A hybridising nucleic acid molecule of the present invention may have a high degree of sequence identity alone its length with a nucleic acid molecule which codes for a polypeptide of the present invention or which is complementary to a nucleic acid molecule which codes for a polypeptide of the present invention (e.g. at least 50%, at least 75% or at least 90% sequence identity). As will be appreciated by the skilled person the higher the sequence identity a given single stranded nucleic acid molecule has with another nucleic acid molecule, the greater the likelihood that it will hybridise to a nucleic acid molecule which is complementary to that other nucleic acid molecule under appropriate conditions.
In view of the foregoing description the skilled person will appreciate that a large number of nucleic acids are within the scope of the present invention. Unless the context indicates otherwise, nucleic acid molecules of the present invention may have one or more of the following characteristics:
1) they may be DNA or RNA;
2) they may be single or double stranded;
3) they may be provided in recombinant form i.e. covalently linked to a 5xe2x80x2 and/or a 3xe2x80x2 flanking sequence to provide a molecule which does not occur in nature;
4) they may be provided without 5xe2x80x2 and/or 3xe2x80x2 flanking sequences which normally occur in nature;
5) they may be provided in substantially pure form (thus they may be provided in a form which is substantially free from contaminating proteins and/or from other nucleic acids);
6) they may be provided with introns (e.g. as a fill length gene) or without introns (e.g. as cDNA).